On the determination of ammonia,by the Folin method,in urines containing crystalline ammonio-magnesium phosphate

Last fall during the progress of the metabolism research that is described in the abstract immediately preceding this, certain anomalous results were obtained in our quantitative determinations of the urinary ammonia. In the earlier periods of that research, urinary ammonia had been determined, by the Folin method, in the urines in duplicate for 38 days, with thoroughly concordant results. Shortly after the beginning of a metabolism period, however, during which magnesium sulfate was injected subcutaneously every twenty four hours, the titrations in duplicate (at the conclusion of the Folin process as applied to the daily urines), were strikingly discordant, the disagreements amounting to from 1 to 2 c.c. of n/5 KOH per 25 c.c. of urine.

Our inability to obtain satisfactory duplicate results for urinary ammonia content after the magnesium sulfate treatment, or to explain the analytic discrepancies by any probable fault of technique, led us to make two general suppositions regarding the cause of the analytic disagreements observed:

1 That magnesium was eliminated into the urines in question in relatively large quantities as ammonio-magnesium phosphate, which separated, in part at least, in typically crystalline masses.

2 That the crystalline ammonio-magnesium phosphate thus deposited was not thoroughly decomposed by sodium carbonate, as used in the Folin process, whereby ammonia, in variable amounts, remained in its solid form as triple phosphate in the urines under investigation.

General examination of the urines that gave the anomalous quantitative results for ammonia content showed at a glance that our first supposition was correct -triple phosphate had crystallized in abundance, In separating portions of the urines for analysis, care had always been taken to isolate fractions of the thoroughly shaken and even mixed daily samples. Consequently, we had no reason to believe that any of the above mentioned anomalous results of the ammonia determinations were due to transferral of unequal amounts of the deposited ammonio-magnesium phosphate in the duplicate fractions of the urine taken. We therefore proceeded to test very carefully, and in many trials, the validity of the second supposition stated above.